Processing plants of this type are mainly designed for coating flexible band substrates, such as, for example, plastics foils, magnetic tapes, films, etc. in vacuum (for example, by sputtering, i.e., target atomization, eventually reinforced by magnetic fields, evaporation, PVD or CVD processes), as well as for additional processing methods, such as pre-processing/cleaning/drying/surface activation/polymerization, etc. It is required, in such cases, to introduce into the plant the band substrates, supplied in the form of bales or foils, which are being placed upon a bearing axle, so that during the coating process, the band substrate may be unrolled from this bale.
Beyond (downstream from the coating chamber(s)), another axle is provided with a take-up reel, upon which the coated band substrate is again being winded.
Basically, such a band coating plant may be split up into modules (unrolling, coating and take-up modules).
On known plants, both axes or cylinders, bilaterally mounted for unrolling and winding up said band substrate, are assembled on a common frame-like base, which offers the advantage that they are in a reciprocal constant and firm positional relationship. When both axes or cylinders are disposed on both sides of the coating module, during the exchange of spools it can be avoided, by means of separate measures, to ventilate also the coating chamber(s) operating in vacuum.
It should be aimed not to ventilate the coating chamber, operating in vacuum, at each exchange of the substrate bale, i.e., when removing from a band substrate a newly rolled up bale, which has just been coated.
It is, therefore, already known to mount air-lock valves between individual modules. The volume which is to be ventilated is thus clearly reduced, since only the intake and removal stations, respectively, are being ventilated and the effective coating chamber may permanently remain in an evacuated condition. Evidently, in case of need, the entire plant may be ventilated.
A known air-lock valve consists of a (pneumatically, hydraulically) inflatable tube or membrane seal, disposed in a passage area of the band substrate. In the inflated condition, the seal is being pressed against the sealing surface, provided beyond the band substrate (preferably elastically flexible), thus firmly gripping the band substrate between itself and said sealing surface.
Although during normal operations the band substrate does not establish contact neither with the tube nor membrane seal, or with said sealing surface, the available passage slot must remain quite narrow, in view of the narrowly limited stroke of the tube or membrane seal. During eventual oscillations of the band substrate during the coating process, contacts may thus occur between said substrate and the border areas of the passage, which, during the evacuation phase from the coating chamber, could result in damages of the coating, which has just been applied. Additionally, due to such undesired contacts, even a rupture of the band substrate under quite high tensile stress may be caused, which again would imply in a forcible paralyzation of the plant.
Problems are also caused by the intense stress of the hollow seal in vacuum, since it is being exposed to extreme pressure differences. Therefore, its wall section (membrane or tube) must be built quite firmly, which again negatively affects its flexibility. Consequently, seal deficiencies may result in the marginal seal area, especially at points where it overlaps the borders of the band substrate (a type of wedge is being formed there, whose surface should evidently be minimized, according to the possibilities).
Lastly, with this known form of seal, the unilateral atmospheric pressure (from the respectively ventilated chamber) acts upon the seal, forcing it into the vacuum chamber.
Document DE 199 12 707 A1 describes a processing plant for a plane, for example, band-like substrates. Two revolving bands pass through its (evacuable) housing, contacting each other in the areas of the passages to introduce and remove the substrate, or including the plane substrate, which they transport between themselves. A sufficient sealing effect is being obtained here due to the spatial contact of both bands with the substrate, but resulting in an extremely reduced width of the passage gap and in a constant superficial contact of said substrate with the conveyor belts.
Document DE 199 60 751 A1 describes another air-lock of this type, which essentially comprises two cylinders with flexible, tube-like casings, which contact each other and between which a band substrate may pass. To improve the sealing effect and in order to minimize lateral gaps between said cylinders and the borders of the passing substrate, the cylinder casings may be pressurized at least temporarily. During this procedure, they inflate and increase, on one side, the contact pressure upon the substrate, and, on the other side, they largely close said lateral gaps. In the area of the vacuum chamber, the cylinder casing surfaces are being supported with supporting rolls towards the inside of the vacuum chamber, to avoid excessive expansion, which implies a considerable additional effort.
Document DE 44 18 383 C2 comprises a vacuum air-lock, which also operates with two reciprocally contacted cylinders, between which a band substrate may pass through. In this case, the cylinders are merely equipped with a cover of elastic and flexible material.
Also document WO 99/50 472 describes a vacuum band coating plant, in which the band substrate must pass through cylinder air-locks between loading and discharge stations and the effective reaction chamber, said cylinder air locks acting as pressure stages. In one version, it may pass between two cylinders rolling upon each other, and, in another version, it may pass between a cylinder and a fixed sealing block. These cylinder air-locks may be opened, in order to introduce, for example, a new band substrate. For this purpose, either one of the cylinders may be folded out, its rotary axis being mounted foldable around an axis of rotation, or the sealing block will be removed from the cylinder. In a variant with only one cylinder, the band is being transported between the cylinder and sealing block through quite a narrow gap, however open at its end, in order not to be submitted to excessive mechanical stress. A complete sealing cannot be obtained in this variant.